1. Field of the Invention
This invention relates to a mean for propelling payloads along a barrel utilizing compressed gas or combustion products.
2. Description of Prior Art
Conventional guns hurl projectiles along the gun barrel by means of chemical propellants which, when ignited in the breech, create high-pressure gases which expand behind the projectile, accelerating it along the barrel. This method, used in forms of weaponry, from cannons, to rifles and handguns, has a fundamental limitation. Once the projectile reaches a high velocity, its speed approaches a limit corresponding to the velocity of the shock wave of the expanding gas.
In practice, the pressure in a gun barrel typically spikes early in the discharge of the gun so that the projectile experiences a very high acceleration at the beginning of discharge. However, as the projectile proceeds down the barrel of the gun, the pressure head behind the projectile begins to decrease, and thus decreases the force of acceleration. In order to increase range, base bleed projectiles have been developed. Additional propellant contained in the projectile is ignited after exiting the barrel to increase the velocity.
Many schemes have been invented to compensate for the velocity limitations of the conventional gun. In light gas guns, for example, helium or hydrogen is used as the propelling gas, where the shock wave travels much faster than that associated with the combustion product gases of the conventional gun. Thus, theoretically and practically, a light gas gun can achieve higher exit velocities from the same length of barrel than can conventional chemical propellant guns. Light gas guns, however, are somewhat limited in the weight of projectiles that can be launched. In a one-stage light gas gun, the gas is contained in a high-pressure vessel near the breech of the gun, and is injected behind the projectile upon discharge by bursting a pressure diaphragm between the pressure vessel and the barrel.
In an alternate version of the light gas gun, pressure storage tanks are located along the barrel with the release of gas triggered to correspond with the passage of the projectile.
In a two-stage light gas gun, there are two chambers or barrels, a larger one containing un-pressured helium or hydrogen, separated from another small caliber barrel containing the projectile by a frangible disk. A chemical charge is ignited in the aft end of the larger chamber forces a piston along the barrel compressing the light gas to the point where the frangible disk breaks and subjects the breech end of the projectile containing barrel to extremely high pressure.
In another novel means of propulsion, a supersonic ramjet or scramjet principle is used to propel the projectile down a barrel that contains an explosive mixture of gas (e.g., oxygen and hydrogen or methane). The projectile is first accelerated by ignition of the gas mixture behind the projectile and giving it an initial impulse. As the projectile travels down the barrel, the un-ignited gases flow around the projectile and are ignited by pressure waves at the base of the projectile, and thus continue the acceleration of the projectile down the barrel. The projectile literally flies supersonically down the barrel of the gun. Although this method overcomes, in principal, the limitation of an expanding gas, as described above, is has practical limitations which to date has limited its application beyond that of laboratory curiosity.
Other non-chemical or compressed gas means of propulsion include electrical or electromagnetic launch schemes. In the so-called rail gun, the barrel consists of two or more rails that are capable of supporting very high current electrical discharge. The projectile essentially shorts out the rails when high voltage is applied, creating a conductive plasma behind the projectile, resulting in an accelerating electromagnetic force that drives the projectile down the barrel. This method of launch suffers from a number of technical challenges. It requires a very large electrical pulse network to feed the rails. Furthermore, erosion of the rails during the launch of the projectile limits the life of the system to a small number of “shots” before the rails need refurbishment.
In an alternate approach, strong magnetic coils are activated along the barrel creating an accelerating magnetic force that propels the payload down the barrel. This coil gun approach also suffers from practical problems associated with the large and costly electrical pulse networks required to fire the projectile, large power switching, as well as, inefficiencies in the transfer of energy from magnetic to linear motion.
In a hybrid chemical/electromagnetic gun, a chemical charge is first ignited in the breech of the gun, with electrodes in the breech simultaneously conducting a heavy electrical discharge that further energizes the plasma driving the projectile down the barrel. This system extends the accelerating force by continuing to feed the plasma energetically. It is, however, limited by the same principals that limit the conventional gun, that is, the projectile velocity is limited by velocity of the shock front of the propelling gas or plasma.
Needs exist for improved accelerating of projectiles through the barrels.